ITU V-Series
Encyclopedia
The ITU-T
V-Series Recommendations on Data communication over the telephone network specify the protocols that govern approved modem
communication standards and interfaces.
Note: the bis
and ter
suffixes are ITU-T standard designators of successive iterations of a standard (bis and ter are derived from the Latin
for 'twice' and 'thrice').
ITU-T
The ITU Telecommunication Standardization Sector is one of the three sectors of the International Telecommunication Union ; it coordinates standards for telecommunications....
V-Series Recommendations on Data communication over the telephone network specify the protocols that govern approved modem
Modem
A modem is a device that modulates an analog carrier signal to encode digital information, and also demodulates such a carrier signal to decode the transmitted information. The goal is to produce a signal that can be transmitted easily and decoded to reproduce the original digital data...
communication standards and interfaces.
Note: the bis
BIS
Bis is a prefix or suffix designating the second instance of a thing, thus preceding ter.Bis can also refer to:* Bis , a Scottish pop band* Bis , a high-teens' magazine published by Kobunsha of Japan...
and ter
Ter
Ter is a prefix or suffix designating the third instance of a thing, thus following bis and preceding quater.Ter can also refer to:* River Ter, in Essex;* Ter , the debut album of American rock band Sweet Water...
suffixes are ITU-T standard designators of successive iterations of a standard (bis and ter are derived from the Latin
Latin
Latin is an Italic language originally spoken in Latium and Ancient Rome. It, along with most European languages, is a descendant of the ancient Proto-Indo-European language. Although it is considered a dead language, a number of scholars and members of the Christian clergy speak it fluently, and...
for 'twice' and 'thrice').
General standards
Applies to V.1–V.9- V.1 is an ITU-T recommendation, entitled Equivalence between binary notation symbols and the significant conditions of a two-condition code.
- V.2 is an ITU-T recommendation, approved in November 1988, titled Power levels for data transmission over telephone lines.
- V.4 is an ITU-T recommendation, approved in November 1988, titled General structure of signals of International Alphabet No. 5 code for character oriented data transmission over public telephone networks.
- V.5 was an ITU-T recommendation, approved in November 1988, titled Standardization of data signalling rates for synchronous data transmission in the general switched telephone network. It has been withdrawn since.
- V.6 was an ITU-T recommendation, approved in November 1988, titled Standardization of data signalling rates for synchronous data transmission on leased telephone-type circuits. It has been withdrawn since.
- V.7 is an ITU-T recommendation, approved in November 1988, titled Definitions of terms concerning data communication over the telephone network.
- V.8 is an ITU-T recommendation, first approved in September 1994, titled Procedures for starting sessions of data transmission over the public switched telephone network. It has been superseded three times. The current version was approved in November 2000.
- V.8bis is an ITU-T recommendation, first approved in August 1996, titled Procedures for the identification and selection of common modes of operation between data circuit-terminating equipments (DCEs) and between data terminal equipments (DTEs) over the public switched telephone network and on leased point-to-point telephone-type circuits. It has been superseded twice. The current version was approved in November 2000.
Interfaces and voiceband modems
Applies to V.10–V.34- V.10 is a ITU-T recommendation, first agreed in 1976, for unbalanced electrical circuits for data communication at up to 100 kbitKilobitThe kilobit is a multiple of the unit bit for digital information or computer storage. The prefix kilo is defined in the International System of Units as a multiplier of 103 , and therefore,...
/s. It can interwork with V.28, provided it is not exposed to signals greater than 12 volts. Used with the 37-pin ISO 4902 connector, it is compatible with EIA RS423. - V.11 is an ITU-T recommendation, first agreed in 1976, for balanced electrical circuits for data communication at up to 10 MbitMegabitThe megabit is a multiple of the unit bit for digital information or computer storage. The prefix mega is defined in the International System of Units as a multiplier of 106 , and therefore...
/s. Used with the 37-pin ISO 4902 connector, it is compatible with EIA-422EIA-422RS-422 is a technical standard that specifies electrical characteristics of a digital signalling circuit. Differential-mode signals can be sent at rates as high as 10 million bits per second, or may be sent on cables as long as 1200 metres. Some systems directly interconnect using RS 422 signals,...
. The 15-pin ISO 4903 connector is recommended for data network interface. - V.17 is an ITU-T faxFaxFax , sometimes called telecopying, is the telephonic transmission of scanned printed material , normally to a telephone number connected to a printer or other output device...
protocolCommunications protocolA communications protocol is a system of digital message formats and rules for exchanging those messages in or between computing systems and in telecommunications...
that uses TCMTrellis modulationIn telecommunication, trellis modulation is a modulation scheme which allows highly efficient transmission of information over band-limited channels such as telephone lines...
modulationModulationIn electronics and telecommunications, modulation is the process of varying one or more properties of a high-frequency periodic waveform, called the carrier signal, with a modulating signal which typically contains information to be transmitted...
at 12 and 14.4 kbit/s. - V.21 is an ITU-T recommendation for full-duplexDuplex (telecommunications)A duplex communication system is a system composed of two connected parties or devices that can communicate with one another in both directions. The term multiplexing is used when describing communication between more than two parties or devices....
communication between two analogueAnalog signalAn analog or analogue signal is any continuous signal for which the time varying feature of the signal is a representation of some other time varying quantity, i.e., analogous to another time varying signal. It differs from a digital signal in terms of small fluctuations in the signal which are...
dial-up modemModemA modem is a device that modulates an analog carrier signal to encode digital information, and also demodulates such a carrier signal to decode the transmitted information. The goal is to produce a signal that can be transmitted easily and decoded to reproduce the original digital data...
s using audio frequency-shift keying modulationModulationIn electronics and telecommunications, modulation is the process of varying one or more properties of a high-frequency periodic waveform, called the carrier signal, with a modulating signal which typically contains information to be transmitted...
at 300 baudBaudIn telecommunications and electronics, baud is synonymous to symbols per second or pulses per second. It is the unit of symbol rate, also known as baud rate or modulation rate; the number of distinct symbol changes made to the transmission medium per second in a digitally modulated signal or a...
to carry digitalDigitalA digital system is a data technology that uses discrete values. By contrast, non-digital systems use a continuous range of values to represent information...
dataDataThe term data refers to qualitative or quantitative attributes of a variable or set of variables. Data are typically the results of measurements and can be the basis of graphs, images, or observations of a set of variables. Data are often viewed as the lowest level of abstraction from which...
at 300 bit/s. It is a variant of the original Bell 103 modulation format. - V.22 is an ITU-T recommendation for full-duplexDuplex (telecommunications)A duplex communication system is a system composed of two connected parties or devices that can communicate with one another in both directions. The term multiplexing is used when describing communication between more than two parties or devices....
communication between two analogueAnalog signalAn analog or analogue signal is any continuous signal for which the time varying feature of the signal is a representation of some other time varying quantity, i.e., analogous to another time varying signal. It differs from a digital signal in terms of small fluctuations in the signal which are...
dial-up modemModemA modem is a device that modulates an analog carrier signal to encode digital information, and also demodulates such a carrier signal to decode the transmitted information. The goal is to produce a signal that can be transmitted easily and decoded to reproduce the original digital data...
s using PSKPhase-shift keyingPhase-shift keying is a digital modulation scheme that conveys data by changing, or modulating, the phase of a reference signal ....
modulationModulationIn electronics and telecommunications, modulation is the process of varying one or more properties of a high-frequency periodic waveform, called the carrier signal, with a modulating signal which typically contains information to be transmitted...
at 600 baudBaudIn telecommunications and electronics, baud is synonymous to symbols per second or pulses per second. It is the unit of symbol rate, also known as baud rate or modulation rate; the number of distinct symbol changes made to the transmission medium per second in a digitally modulated signal or a...
to carry data at 1200 or 600 bit/s. It is a variant of the Bell 212ABell 212AThe Bell 212A modulation scheme defined a standard method of transmitting full-duplex asynchronous serial data at 1.2 kbit/s over analogue transmission lines. The equivalent, but incompatible ITU-T standard is V.22....
modulation format. - V.22bis is an ITU-T recommendation extending V.22 with a faster rate using QAMQuadrature amplitude modulationQuadrature amplitude modulation is both an analog and a digital modulation scheme. It conveys two analog message signals, or two digital bit streams, by changing the amplitudes of two carrier waves, using the amplitude-shift keying digital modulation scheme or amplitude modulation analog...
modulationModulationIn electronics and telecommunications, modulation is the process of varying one or more properties of a high-frequency periodic waveform, called the carrier signal, with a modulating signal which typically contains information to be transmitted...
at 600 baudBaudIn telecommunications and electronics, baud is synonymous to symbols per second or pulses per second. It is the unit of symbol rate, also known as baud rate or modulation rate; the number of distinct symbol changes made to the transmission medium per second in a digitally modulated signal or a...
to carry digitalDigitalA digital system is a data technology that uses discrete values. By contrast, non-digital systems use a continuous range of values to represent information...
dataDataThe term data refers to qualitative or quantitative attributes of a variable or set of variables. Data are typically the results of measurements and can be the basis of graphs, images, or observations of a set of variables. Data are often viewed as the lowest level of abstraction from which...
at 2400 or 1200 bit/s. The 1200 bit/s mode is compatible with V.22. - V.23 is an ITU-T recommendation for half-duplexDuplexDuplex commonly means double or twofold.It may also refer to:* Duplex , a two-unit apartment building or condominium* Duplex, a common electrical receptacle with two NEMA type 5 plugs* Duplex locomotive, a type of steam locomotive...
communication between two analogueAnalog signalAn analog or analogue signal is any continuous signal for which the time varying feature of the signal is a representation of some other time varying quantity, i.e., analogous to another time varying signal. It differs from a digital signal in terms of small fluctuations in the signal which are...
dial-up modemModemA modem is a device that modulates an analog carrier signal to encode digital information, and also demodulates such a carrier signal to decode the transmitted information. The goal is to produce a signal that can be transmitted easily and decoded to reproduce the original digital data...
s using FSKFrequency-shift keyingFrequency-shift keying is a frequency modulation scheme in which digital information is transmitted through discrete frequency changes of a carrier wave. The simplest FSK is binary FSK . BFSK uses a pair of discrete frequencies to transmit binary information. With this scheme, the "1" is called...
modulationModulationIn electronics and telecommunications, modulation is the process of varying one or more properties of a high-frequency periodic waveform, called the carrier signal, with a modulating signal which typically contains information to be transmitted...
at up to 600 or 1200 baudBaudIn telecommunications and electronics, baud is synonymous to symbols per second or pulses per second. It is the unit of symbol rate, also known as baud rate or modulation rate; the number of distinct symbol changes made to the transmission medium per second in a digitally modulated signal or a...
to carry digitalDigitalA digital system is a data technology that uses discrete values. By contrast, non-digital systems use a continuous range of values to represent information...
dataDataThe term data refers to qualitative or quantitative attributes of a variable or set of variables. Data are typically the results of measurements and can be the basis of graphs, images, or observations of a set of variables. Data are often viewed as the lowest level of abstraction from which...
at up to 600 or 1200 bit/s respectively. An optional 75 baud reverse channel carries 75 bitBitA bit is the basic unit of information in computing and telecommunications; it is the amount of information stored by a digital device or other physical system that exists in one of two possible distinct states...
/s. - V.24 is referenced as RS-232RS-232In telecommunications, RS-232 is the traditional name for a series of standards for serial binary single-ended data and control signals connecting between a DTE and a DCE . It is commonly used in computer serial ports...
which also includes V.28. - V.250 (also known as V.25ter) is extended data modems ITU-T recommendation .
- V.27ter is an ITU-T recommendation for a half-duplex modemModemA modem is a device that modulates an analog carrier signal to encode digital information, and also demodulates such a carrier signal to decode the transmitted information. The goal is to produce a signal that can be transmitted easily and decoded to reproduce the original digital data...
, allowing 2400 and 4800 bit/s (PSKPhase-shift keyingPhase-shift keying is a digital modulation scheme that conveys data by changing, or modulating, the phase of a reference signal ....
modulation). - V.28 is an ITU-T recommendation defining the electrical characteristics for unbalanced double-current interchange circuits.
- V.29 is an ITU-T recommendation for a modemModemA modem is a device that modulates an analog carrier signal to encode digital information, and also demodulates such a carrier signal to decode the transmitted information. The goal is to produce a signal that can be transmitted easily and decoded to reproduce the original digital data...
, allowing 4.8 kbit/s, 7.2 kbit/s and 9.6 kbit/s transfer modes (PSKPhase-shift keyingPhase-shift keying is a digital modulation scheme that conveys data by changing, or modulating, the phase of a reference signal ....
and QAM modulations). - V.32 is an ITU-T recommendation for a modemModemA modem is a device that modulates an analog carrier signal to encode digital information, and also demodulates such a carrier signal to decode the transmitted information. The goal is to produce a signal that can be transmitted easily and decoded to reproduce the original digital data...
operating as full-duplex on a 4-wire circuit, or half-duplex on a two-wire circuit, allowing bidirectional data transfer at either 9.6 kbit/s or 4.8 kbit/s at a symbol rateSymbol rateIn digital communications, symbol rate is the number of symbol changes made to the transmission medium per second using a digitally modulated signal or a line code. The Symbol rate is measured in baud or symbols/second. In the case of a line code, the symbol rate is the pulse rate in pulses/second...
of 2,400 baudBaudIn telecommunications and electronics, baud is synonymous to symbols per second or pulses per second. It is the unit of symbol rate, also known as baud rate or modulation rate; the number of distinct symbol changes made to the transmission medium per second in a digitally modulated signal or a...
instead of the 600 baudBaudIn telecommunications and electronics, baud is synonymous to symbols per second or pulses per second. It is the unit of symbol rate, also known as baud rate or modulation rate; the number of distinct symbol changes made to the transmission medium per second in a digitally modulated signal or a...
of the V.22 standards. - V.32bis is an ITU-T recommendation for a modemModemA modem is a device that modulates an analog carrier signal to encode digital information, and also demodulates such a carrier signal to decode the transmitted information. The goal is to produce a signal that can be transmitted easily and decoded to reproduce the original digital data...
, allowing up to 14.4 kbit/s bidirectional data transfer. Other additional defined data transfer rates are 12.0 kbit/s, 9.6 kbit/s, 7.2 kbit/s, and 4.8 kbit/s. The standard was extended by several modem manufacturers to allow bidirectional data transfer rates of 19.2 kbit/s, but never ratified as a V.32ter standard. These non-ITU-T standard modems were often referred to as 'V.32terbo' modems. - V.33 is an ITU-T recommendation for a modemModemA modem is a device that modulates an analog carrier signal to encode digital information, and also demodulates such a carrier signal to decode the transmitted information. The goal is to produce a signal that can be transmitted easily and decoded to reproduce the original digital data...
operating as full-duplex on a 4-wire point-to-point leased line allowing bidirectional data transfer at either 14.4 kbit/s. - V.34 (09/94) is an ITU-T recommendation (superseded) for a modemModemA modem is a device that modulates an analog carrier signal to encode digital information, and also demodulates such a carrier signal to decode the transmitted information. The goal is to produce a signal that can be transmitted easily and decoded to reproduce the original digital data...
, allowing up to 28.8 kbit/s bidirectional data transfer. Other additional defined data transfer rates are 24.0 kbit/s and 19.2 kbit/s as well as all the permitted V.32 and V.32bis rates. It is the successor to the unofficial V.FC (V.Fast Class; also known as V34draft) standard created by HayesHayes Microcomputer ProductsHayes Microcomputer Products was a U.S.-based manufacturer of modems. They are particularly well known for their Smartmodem, which is introduced the ability to control the modem through commands sent in the data stream itself. The "smart modem" approach dramatically simplified operation, making...
and RockwellConexantConexant Systems, Inc. is an American semiconductor company, formerly the semiconductor division of Rockwell International. Currently it's privately owned by Golden Gate Capital, an equity firm headquartered in San Francisco.-History:...
, which was the first widely available 28.8 kbit/s protocol. Most V.34 modems support V.FC, although not all modern modems support both. Additionally, V.34 modems employ shell mapping as shaping codeShaping codesIn digital communications shaping codes are a method of encoding that changes the distribution of signals to improve efficiency.-Description:...
to reduce the transmit power. - V.34 (10/96) is an updated ITU-T recommendation for a modem, building on the V.34 standard but allowing up to 33.8 kbit/s bidirectional data transfer. Other additional defined data transfer rates are 33.6, 31.2 kbit/s, as well as all the permitted V.34 rates. Modems implementing this standard were often marketed under the moniker V.34+. It was later superseded by V.34 (02/98), commonly rendered as V.34bis, which corrected some errata in the original 1996 document, and capped the speed to 33.6 kbit/s.
Wideband modems
Applies to V.35–V.39- V.35 is an ITU-T standard located on layer 1 on the OSI modelOSI modelThe Open Systems Interconnection model is a product of the Open Systems Interconnection effort at the International Organization for Standardization. It is a prescription of characterizing and standardizing the functions of a communications system in terms of abstraction layers. Similar...
. Max speed is 2 Mbit/s. Withdrawn ITU-T recommendation for 48 kbit/s data transmission over wideband circuits. The physical and electrical characteristics of this interface are now specified in ITU-T recommendation V.11.
Error control and data compression
Applies to V.40–V.49- V.41 is a code-independent error control system. Defines the ITU-TITU-TThe ITU Telecommunication Standardization Sector is one of the three sectors of the International Telecommunication Union ; it coordinates standards for telecommunications....
standard CRC-16Cyclic redundancy checkA cyclic redundancy check is an error-detecting code commonly used in digital networks and storage devices to detect accidental changes to raw data...
polynomial as x16 + x12 + x5 + 1 - V.42 is an error correction protocol. Its function is to allow the receiver to immediately request re-transmission of any lost data packets. However, it does not guarantee how quickly the error-free data will be delivered to the receiving end. V.42 is generally included in dialup modems. Also defines the ITU-T standard CRC-32 polynomial as x32+x26+x23+x22+x16+x12+x11+x10+x8+x7+x5+x4+x2+x+1, and includes the LAPMLAPMLink Access Procedure for Modems is part of the V.42 error correction protocol for modems.LAPM is an error control protocol defined in ITU-T recommendations V.42. Like many data link layer protocols, it is a variant of HDLC...
framing protocol. - V.42bis, also an adaptive data compression standard, is based on the Lempel Ziv dynamic dictionary approach, and may go to "transparent mode," in which data is transmitted uncompressed. The specific algorithm is "BTLZ" (British Telecom Lempel Ziv), which was developed by Alan Clark (then with BT, now with Telchemy).
- V.44 is based on LZJH (Lempel-Ziv-Jeff-Heath) adaptive data compression developed by Hughes Electronics for its DirecPC satellite Internet, and incorporated into the v.92 dial-up modem standard. V.44 offers somewhat better compression performance for certain types of data than the V.42bis standard, on average allowing 15% greater throughput. For instance, a 53.3 kbit/s connection with V.44 can transmit up to 53.3×6 = 320 kbit/s using pure text. In reality, the overall data rate rarely exceeds 3:1 compression (~150 kbit/s). It should be noted that the compression tends to get better and worse over time due to noise on the line, or due to the transfer of already-compressed files (ZIP files, JPEG images, MP3 audio, MPEG video). At some points the modem will be sending compressed files at 53 kbit/s, uncompressed files at 160 kbit/s, and pure text at 320 kbit/s, or any value in between.
Simultaneous transmission of data and other signals
Applies to V.60–V.99- V.61V.61ITU V.61 is a standard for Analog Simultaneous Voice and Data , a MODEM related standard for use over a POTS line or leased line.The can be downloaded free of charge in several languages.-See also:*V.70 Digital Simultaneous Voice and Data...
Analog Simultaneous Voice and Data (ASVD) - V.70 Digital Simultaneous Voice and Data (DSVD)
- V.80: videoconferencingVideoconferencingVideoconferencing is the conduct of a videoconference by a set of telecommunication technologies which allow two or more locations to interact via two-way video and audio transmissions simultaneously...
. It is generally compatibilized with H.324 standard point-to-point video telephony over regular phone lines. - V.90 is an ITU-T recommendation for a modemModemA modem is a device that modulates an analog carrier signal to encode digital information, and also demodulates such a carrier signal to decode the transmitted information. The goal is to produce a signal that can be transmitted easily and decoded to reproduce the original digital data...
, allowing 56 kbit/s download and 33.6 kbit/s upload. It replaced two vendor standards (K56flex and X2) and was designed to allow modems from both prior standards to be flash upgraded to support it. It was developed between March 1998 and February 1999. It is also known as V.Last as it was anticipated to be the last standard for modems operating near the channel capacity of POTSPlain old telephone servicePlain old telephone service is the voice-grade telephone service that remains the basic form of residential and small business service connection to the telephone network in many parts of the world....
lines to be developed. V.90 is generally used in concert with the V.42bis compression standard. A follow-on standard, V.92V.92V.92 is an ITU-T recommendation, titled Enhancements to Recommendation V.90, that establishes a modem standard allowing near 56 kb/s download and 48 kb/s upload rates. With V.92 PCM is used for both the upstream and downstream connections; previously 56K modems only used PCM for downstream...
, was developed later in 1999 to replace V.90. - V.92V.92V.92 is an ITU-T recommendation, titled Enhancements to Recommendation V.90, that establishes a modem standard allowing near 56 kb/s download and 48 kb/s upload rates. With V.92 PCM is used for both the upstream and downstream connections; previously 56K modems only used PCM for downstream...
is an ITU-TITU-TThe ITU Telecommunication Standardization Sector is one of the three sectors of the International Telecommunication Union ; it coordinates standards for telecommunications....
recommendation, titled Enhancements to Recommendation V.90, that establishes a modemModemA modem is a device that modulates an analog carrier signal to encode digital information, and also demodulates such a carrier signal to decode the transmitted information. The goal is to produce a signal that can be transmitted easily and decoded to reproduce the original digital data...
standard allowing 56 kbit/s download, 48 kbit/s upload rates, and the new V.44 compression method. V.92 was first presented in August 1999. It is intended to succeed the V.90 standards. With V.92, PCMPulse-code modulationPulse-code modulation is a method used to digitally represent sampled analog signals. It is the standard form for digital audio in computers and various Blu-ray, Compact Disc and DVD formats, as well as other uses such as digital telephone systems...
is used for both the upstream and downstream connections; previously 56K modems only used PCM for downstream data.
Interworking with other networks
Applies to V.100–V.199- V.110 is an ITU-T recommendation for using terminal adaptor functions for the connection of terminals having interfaces conforming to V-series to the ISDN.
- V.120 is an extension for V.110 that includes statistical multiplexing.
- V.150.1 is an ITU-T recommendation for using a modemModemA modem is a device that modulates an analog carrier signal to encode digital information, and also demodulates such a carrier signal to decode the transmitted information. The goal is to produce a signal that can be transmitted easily and decoded to reproduce the original digital data...
over IP networks.
Interface layer specifications for data communication
Applies to V.200–V.249- V.230 is an ITU-T recommendation, approved in November 1988, titled General data communications interface layer 1 specification.
Digital circuit modems
Applies to V.300–V.399- V.300 is an ITU-T recommendation, first approved in July 1999, titled A 128 (144) kbit/s data circuit-terminating equipment standardized for use on digital point-to-point leased circuits.
See also
- ITU-TITU-TThe ITU Telecommunication Standardization Sector is one of the three sectors of the International Telecommunication Union ; it coordinates standards for telecommunications....
- 56 kbit/s modem
- Microcom Networking ProtocolMicrocom Networking ProtocolThe MNP family of error-correcting protocols were commonly used on early high-speed modems. Originally developed for use on Microcom's own family of modems, the protocol was later openly licensed and used by most of the modem industry, notably the "big three", Telebit, USRobotics and Hayes...
s (MNP1 to 10) - List of device bandwidths
External links
- ITU-T Recommendations: V Series
- V.35 Technical Info – Includes pinouts and history
- V.44 FAQ
- Technical information on the LZJH algorithm in use in the V.44 standard
- Basic handshakes & modulations – V.22, V.22bis & V.32 handshakes